Concrete blocks have been a basic building material for many years. Concrete blocks have been designed for use in many applications, including concrete retaining wall blocks used to construct retaining walls. Concrete retaining wall blocks are typically dry stacked (i.e. no mortar is used) in ascending courses.
A concrete block is sometimes formed with one or more core openings. This lightens the block thereby make the manual handling of the block easier, and reduces the amount of material used to form the block thereby reducing material costs. The core opening(s) can extend entirely through the block from the top of the block to the bottom, or partially through the block (e.g. extending from the bottom of the block toward the top but not extending through the top).
An example of the formation of core openings in a concrete retaining wall block is disclosed in U.S. Pat. No. 5,827,015. As disclosed in that patent, and with reference to FIG. 6 herein, a pair of concrete retaining wall blocks are formed face-to-face within a mold 100 that has an open top and an open bottom and is positioned on a pallet 102. The tops of the resulting blocks rest on the pallet and the bottom of the blocks face upward. For each block, a pair of core forms 104 are positioned within the mold 100 to form a pair of core openings in each of the resulting blocks. Dry-cast concrete is then deposited in the mold 100, the mold is vibrated to densify the dry-cast concrete, and a head 106 or “stripper-shoe” is brought down into the mold to compress the concrete in the mold and form the resulting bottom surfaces of the blocks. Thereafter, the blocks are stripped from the mold through relative vertical movement of the pallet 102 and mold 100 assisted by the head 106 pushing the blocks out of the mold. As the blocks are stripped from the mold, the core forms 104, which are fixed to the mold, strip from the concrete, leaving behind the core openings in the blocks.
When a cored retaining wall block is stripped from the mold, a small ridge of concrete tends to be left around the edge of the core opening at what will be the bottom surface of the block (termed “feathering”). Similar feathering tends to occur along other edges of what will be the bottom surface of the block that are in contact with mold surfaces, for example the bottom side edges of the block. Once solidified, feathering can interfere with the block laying flat on other blocks when dry-stacked in a wall.
Attempts to remove the feathering have included the use of a rotating brush on the production line after the block is stripped from the mold to sweep away feathering that occurs. However, it has been found that the brush often leaves some of the feathering, particularly feathering that occurs along an edge that is perpendicular to the rotational axis of the brush.
There is a need for methods and equipment that minimize the feathering that occurs along bottom edges on concrete blocks as a result of the blocks being stripped from the mold.